“Today’s complex and high node count printed circuit (PC) boards can be difficult to test. To accurately detect, diagnose and repair their manufacturing faults, several manufacturers test these PC boards with multiple types of test systems. This multiple test style environment combines two or more different types of PC board testers. Currently one strategy combines automatic x-ray inspection with a modification of traditional in-circuit testing.

This strategy changes the test department’s overall test paradigm, and has significant impacts on design for testability guidelines for these complex, high node count PC boards. New guidelines need to be established to ensure efficient testing of PC boards with automatic x-ray systems, while also preserving in-circuit requirements that persist. These design guidelines can also assist in providing for selective access removal in cases where automatic x-ray systems provide efficient testing capability.

This paper proposes, examines and summarizes new design for testability guidelines for a combined x-ray/in-circuit testing environment. The paper reviews and updates rules to help test and design engineers provide high-yield processes for x-ray inspection and in-circuit test of PC boards. It also presents guidelines which take advantage of this combined test strategy to reduce required in-circuit probing accessibility, redundancy of test across test systems, and maximizing test efficiency while lowering per unit cost of test.

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